Not Applicable
Not Applicable
1. Field of the Invention
The invention relates to a method and an arrangement for linearizing a radio receiver. The invention can be advantageously applied in the reception circuits of mobile stations.
2. Description of the Related Art Including Information Disclosed Under 37 C.F.R 1.97 and 1.98.
The quality of a signal in a radio receiver is degraded by noise and interference added to the signal on the transmission path, noise in the reception circuitry, as well as by noise and interference indirectly caused by other radio signals. The latter refers to a situation in which a signal on a neighboring channel, which momentarily is considerably stronger than the signal to be received, shifts the operating point of the high-frequency amplifier and/or mixer towards non-linearity and saturation. This degrades the signal-to-noise ratio at the amplifier output. In the mixer the increase of non-linearity will intensify intermodulation products and, thus, increase the overall noise and interference level.
A basic method for reducing noise and interference is filtering, which takes place in all receivers in many stages of operation and which will not be discussed further in this description. Rather, we will discuss the widening of the linear range of amplifiers and mixers as a means of reducing noise and interference. The linear range gets wider as the operating voltage is increased or, if the operating voltage remains unchanged, as the supply current is increased. So, the signal quality can be improved by using more energy in the receiver. In the prior art, said circuits are specified such that the signal quality requirements will be met even in poor noise and interference conditions. A disadvantage of this method, as regards portable devices, is that it requires a relatively large supply of energy and, therefore, shortens the battery life.
From the prior art it is also known a method in which the strength of the received signal is monitored and the supply current of the mixer is increased if the strength of the signal drops. An advantage of the method is that it improves the quality of the signal and reduces intermodulation products if the field received is weak. A disadvantage, however, is that the supply current will be increased even if the receiver received no other, interfering, signals. Moreover, the amplifiers have to be rated for the worst case, which results in a relatively large continuous current consumption in the amplifiers.
The object of the invention is to reduce the aforementioned disadvantages related to the prior art.
The basic idea of the invention is as follows: A receiver monitors the signal strength on the receive channel and neighboring channels. In addition, the receiver can determine the quality of the detected signal by calculating its bit error ratio or signal-to-noise ratio. In normal conditions, i.e. when the signal strength is satisfactory on the receive channel and ordinary on the neighboring channels, the supply currents of the receiver""s front-end amplifiers and at least the first mixer are kept relatively low. If the signal strength goes below a certain value on the receive channel or exceeds a certain value on a neighboring channel, said supply currents are increased. This may happen also if the bit error ratio or signal-to-noise ratio deteriorates down to a certain limit. Adjustment of the supply currents may take place in one or more steps.
The advantage of the invention is that the energy consumption of the receiver can be reduced without degrading the signal quality. This means longer life for the battery or, if the life of the battery is kept unchanged, that a smaller battery can be used. If the mean energy consumption is kept the same as in receivers of the prior art, the advantage is a better signal quality.
The method according to the invention for linearizing a radio receiver in a signal chain in which
a signal received from an antenna is amplified and the amplified signal is detected, and
the received signal is processed by at least one linear unit is characterized in that
at least one quality factor of the detected signal is measured, and
the supply current of said at least one linear unit is controlled on the basis of the measurement results.
The arrangement according to the invention for linearizing a radio receiver comprising means for detecting a received signal and at least one linear unit with current supply circuits for processing the received signal is characterized in that it comprises
means for measuring at least one quality factor of the detected signal, and
means for controlling the linear unit""s supply current on the basis of the measurement results.